1. Cell Structure and Function
Cell Boundaries

2. What is the cell membrane?
Click the picture to access interactive activity for cell membrane
All cells are surrounded by a thin, flexible barrier made of phospholipids known as the cell membrane.
Regulates what enters and leaves the cell.
Provides protection and support.
Semipermeable: Some molecules can go through while others cannot.

3. Why cells look like they do?
What happens when oil is poured in water?
Water and oil will separate because water is a polar molecule and oil is nonpolar
The cell membrane is shaped by the interaction of water found inside and outside of the cell and the phospholipids that form the cell membrane.

4. How are cell membranes constructed?
Basic building block of the cell membrane is a kind of lipid molecule called a phospholipid.
The head contains phosphorous, which make it polar.
Hydrophilic head
The long tails of fatty acids are nonpolar.
Hydrophobic tails

5. How are cell membranes constructed?
Water can interact with the polar heads and repel the nonpolar lipids tails.
The polar heads of the phospholipids point toward the water inside and outside the cell.
The tails are buried in the interior of the membrane, directing themselves away from the water.
This double layer of phospholipids forms a flexible lipid bilayer.

6. What else is There?
In addition to lipids, most cell membranes contain protein molecules that are embedded in the lipid bilayer.
Proteins form channels and pumps that help to move material across the cell membrane.
Carbohydrate molecules are attached to many of these proteins.
Act like chemical identification cards, allowing cells to identify one another.

7. How does the membrane regulate movement of substances?
Large molecules will not pass due to their size
Polar molecules will not pass because they will not interact with the hydrophobic (nonpolar) tails of the lipids.
Water can pass even though it is polar (very small)
oxygen and carbon dioxide are small, nonpolar molecules and pass with ease

8. What are protein channels and Carriers?
Proteins channels are formed by doughnut-shaped proteins.
Act as passageways through which only certain molecules can pass.
Each channel will admit only certain molecules
Protein carriers are proteins that carry molecules from one side of the membrane to another
Both channels and carriers use no energy
Channel
Carrier

9. What is that Smell?
What happens when a bottle of perfume is opened at the front of a room?
Within minutes people further and further from the source can smell the perfume.
Why?
Because perfume molecules are more concentrated in the bottle, molecules inside the bottle move to a less concentrated space outside the bottle.

10. What is diffusion? (passive transport)
Particles in a solution are in constant, random motion. Because of this, they tend to move from an area where they are more concentrated to an area where they are less concentrated by a process called diffusion.
When the concentration of the solute is the same throughout a system, the system has reached equilibrium. The molecules are now moving equally from one side to the other.
Because diffusion depends upon particle movements, substances diffuse across membranes without requiring the cell to use energy.
Movement of solute
(no energy required)
Low concentration
High concentration

11. What is osmosis?(passive transport)
Osmosis is the diffusion of water through a selectively permeable membrane.
If there is a difference in concentration of H2O, there will be a net movement of H2O to the side with less water until equilibrium is reached.

12. Isotonic solution: the solute concentration of the solution and cell is the same.
Hypertonic solution: A solution that has a solute concentration greater than a cell placed in the solution
Hypotonic solution: A solution that has a solute concentration less than a cell placed in the solution
More water/less solutes in the solution.
Less water/more solutes in cell
More water enters the cell than leaves it.
Water is equal inside and outside the cell
Solutes equal on both sides
Water moves into and out of the cell at an equal rate.
Less water/more solutes in solution
More water/less solutes in cell
More water leaves the cell than enters it.

13. What is facilitated diffusion? (passive transport)
Cell membranes have protein channels or carriers that make it easy for certain molecules to cross the membrane in a process known as facilitated diffusion.
Facilitated diffusion does not require the use of cell’s energy.
It uses the movement of the solutes from where they are higher in concentration to lower concentration.

14. What is Active Transport?
Squares have a lower concentration
During active transport cells move materials against their concentration gradient/against the flow of diffusion (less concentration to higher concentration).
Requires energy.
Carried out by transport proteins or pumps found in the cell membrane.
Moves molecules in only one direction.
Squares have a higher concentration

15. What is Active Transport?
Cell Membrane: Active Transport
A Segment of: Cells: The Building Blocks of Life

16. Bulk Transport
Endocytosis is the process of actively transporting molecules into the cell by engulfing it with its membrane.
Exocytosis describes the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell.
Requires energy.

17. Bulk Transport
Endocytosis and Exocytosis Animation